In the recovery of crude oil from subterranean formations, large quantities of oil will generally remain in the formation when production relies solely upon primary depletion, i.e., where only initial formation energy is used to recover the oil. Where the initial formation energy is inadequate or has become depleted, supplemental operations are employed, such operations commonly referred to as secondary recovery operations. In certain of these supplemental recovery operations, a fluid is injected through at least one well, called an injection well, and passed into the formation. The oil is moved through the formation and is produced from another well, called a production well, as the injected fluid passes from the injection well toward the production well.
One of the most widely used secondary recovery operations is waterflooding, wherein water is the fluid passed through the formation. As is well to those skilled in the art, waterflooding operations often employ the use of thickening agents, surfactants and other additives to further increase the recovery of oil.
The cost of processing the water used in waterflooding operations is directly borne by any increased oil production resulting therefrom. In situations where disposal is necessary, there is no compensation for handling the water and the disposal costs are a direct levy against the gross profits from oil production. Waste water has, at best, only minor value and its proper handling is imperative to avoid contamination of surface or underground water. In view of these and other factors, waterflooding operations generally employ recycled produced waters, such waters often better characterized as brines. These brines, which may contain a few hundred to several hundred thousand parts per million of dissolved solids, may be sweet or sour and may be saturated with calcium sulfate, calcium carbonate, and other salts. In systems employing recycled produced water, the water is generally collected in a central storage tank from several batteries, and is often injected back into the formation through a common injection station.
As may be appreciated by those skilled in the art, it is common to have some degree of oil carry-over into water tankage when produced water is used in the waterflooding operation. The same is true for any tankage used to store produced waters for any purpose. Moreover, the cost of the waterflooding operation itself increases proportionally to the amount of produced oil sent back into the ground as part of the waterflooding operation. Additionally, other produced materials, such as iron sulfide, preferentially reside within the produced oil. Should such iron sulfide containing oil be pumped back into the injection well with the injection water, the likelihood of damage to pumps and related equipment increases.
Therefore, what is needed is an economical apparatus and system for the recovery of low density liquids from oil production water tanks.